The methods of zinc extraction can be divided into two main classes, i.e. the methods of Pyro- and Hydro-metallurgy. Electrolytic zinc extraction is processed by hydrometallurgy is accomplished by extracting zinc calcine with sulfuric acid solution and cleaning the extracted solution by a purification process and electrolysing this purified zinc or sulfate solution. Metallic zinc, so called electrolytic zinc is deposited on a cathode.
On the other hand, the method of zinc smelting by pyrometallurgy is called a distillation process and is proceeded by mixing zinc calcine mainly consisting of zinc oxide and a reducing agent and charging them into a retort which is kept at a high temperature. Then, zinc is reduced, vaporized and condensed. The distillation process embodies methods of horizontal distillation, vertical distillation and electro thermic distillation. A smelting method by a blast furnace (I S F process) is utilized as one kind of the pyrometallurgical method. This method, as taught in Japanese Patent No. 194576 (Patent publication Showa 27-No. 4111), explains this kind of smelting method of zinc in a blast furnace. This method has the merit in that zinc and lead are recovered at the same time but has several demerits that is, (1) the charged material must be sintered, (2) exhaust heat from the furnace is difficult to recover and, (3) expensive metallurgical coke is necessary.
To save energy consumption in both hydrometallurgical and pyrometallurgical processing of zinc, many improvements have been made. However, even when applying such improvements to the process of the present invention, the energy saving is low, even less than 10 percent.
The following conditions are necessary for saving energy and cost relating to the method of pyrometallurgical smelting of zinc.
(1) Simple processes and low cost of investment are necessary,
(2) Energy sources, such as heavy oil and lump coke which have high energy cost per calorie should be changed to coke breeze or pulverized powder coal which are materials of low cost per calorie,
(3) The waste energy of exhaust gas or slag should be recovered more effectively;
(4) valuable elements in the zinc calcine should be recovered at high efficiency;
(5) The process should be automatically controlled;
(6) A high production of zinc and effective recovery of by-products from the ore is essential.
Besides these terms, it is obvious that the high production rate of zinc and the effective recovery of the valuable byproducts from the ore are necessary.
Before now, Goto, Ogawa and Takinaka (Abstract Collection of Lectures of the Meeting in Spring of the Japan Mining Society, p. 253, 1979) and H. Abramowitz and Y. K. Rao (Trano Gnst. Min. Met. 87 C180 11978) provide the direct reduction method of the zinc concentrate by CaO and carbon for saving the energy and cost of the pyrometallurgical zinc smelting method but they are not industrialized.